LTE (Long Term Evolution) of 3rd Generation Partnership telecommunication systems Release 10 is supposed to support inband relaying. In this situation a donor eNode B (eNB) communicates to the relay node which in turn exchanges data with a user equipment and the same spectrum is used for the eNodeB-relay and relay-user equipment links. At least the relay-user equipment links shall be backward compatible to Release 8 (Rel-8). A relay node (RN) must avoid self-interference, i.e., while transmitting to a user equipment (UE) it cannot receive from its donor eNB and while receiving from a UE it cannot transmit towards its donor eNB because reception and transmission of the relay node would in both cases be in the same frequency band and can thus not easily be filtered out. Self-interference at the relay can be avoided by dedicating certain subframes to the eNB-RN (Un) link.
In a relay scenario a scheduler in the radio access node, e.g. an eNB, schedules all data transmission and allocates transmission resources to the RNs and UEs in the coverage area. Another scheduler is located in each relay node and allocates transmission resources to its associated UEs. Naturally, a scheduler in the relay node may only allocate resources for Uu transmission that are not scheduled for Un transmission.
Another user equipment can also be directly connected to the eNB and may directly communicate with the eNB without the involvement of the relay node over a Uu interface.
Obviously, the relay operation is different from the operation of a Rel-8 FDD (Frequency Division Duplex) eNB, which can transmit to its UEs in any DL (downlink) subframe. In Rel-8 it is possible to configure certain subframes as MBSFN (Multi-media Broadcast Multicast Service over Single Frequency Network) subframes which indicate to the UEs that they are not supposed to receive data beyond the control region (PCFICH (Physical Control Format Indicator Channel), PDCCH (Physical Downlink Control Channel) and PHICH (Physical HARQ Indicator Channel)) in the first 1-2 symbols of the subframe. Note that MBSFN subframes have less OFDM (Orthogonal Frequency Division Multiplex) symbols available for L1/L2 control than regular subframes. However, MBSFN subframes can only be configured for subframes 1, 2, 3, 6, 7 and 8. In other subframes (0, 4, 5 and 9) at least Rel-8 UEs expect to receive the Broadcast Channel, Synchronization Channels and paging information.
Un subframes affect the HARQ (Hybrid Automatic Repeat Request) timing and the associated control signaling defined for Rel-8. The HARQ feedback is synchronous, i.e., it is sent in subframe n+4 if the corresponding data was received in subframe n. This applies to both uplink (UL, transmission towards the eNB) and downlink DL, (transmission towards the user equipment). On the uplink also the retransmissions are synchronous, i.e., they must appear in subframe n+8. Downlink retransmissions can be scheduled asynchronously, in subframe n+8 or later.
The different periodicities of MBSFN patterns (10 ms or 40 ms) and uplink HARQ (8 ms) precludes Rel-8 conform protocol operation on Un and Uu.
Since the pattern of Un subframes does not match the Rel-8 HARQ timing, a modification of the Un HARQ control handling and a definition for Un subframe allocation are required.